Just curious where everyone is keeping their tires inflated too. Mine came with 30 in the rear and 29 on the front. The manual says put 44 lbs if you gonna go over 100mph and the tire says 51 max psi. I just raised them all to 38 psi cold

Ignore the 51 psi max pressure on the tire for setting operating pressures. Max tire pressure is related to the tire's design basis, not vehicle operation.

I don't know why the video would differ from the manual, but delaying the onset of standing waves in the tread and maintaining tire load capacity are likely involved in the increased pressures . . . tire rated load capacity actually does drop off at very high speeds - Linky.